During the sawing of a steel structural shape with a rotary metal saw the beam or bar having at least one flange lies an a table or roller bed, clamped on a support on which it is fed to the metal sawblade.
The metal saw is operated at a specified speed in terms of number of revolutions per minute (r.p.m.) the blade and workpiece are translatorily relatively displaced at a specified feed speed.
The speed of the feed is determined by the number of r.p.m., the number of saw teeth and the radius of the metal saw.
During the sawing procedure the flange is subjected to a forced elastic deflection by the blade against a force by this action of the saw teeth.
These movements are determined by the tooth succession time (i.e. the time between encounters of successive teeth with the flange) and the speed.
The structural steel shapes can have H,U,I, or T cross section or an angular profile, i.e. a channel I-beam, H-beam, T-beam or angle iron.
The invention is especially advantageous when applied to the cutting of structural steel shapes as they are usually used in steel construction and especially heavy steel construction, and the metal saw is designed for this purpose.
The tooth succession time is, as noted, the small time interval which elapses between successive saw teeth engaging in the cutting procedure while the metal saw is in operation. If the number of r.p.m. within a unit of time is defined as "n" and if the number of teeth is defined as "x", then the tooth succession time is the reciprocal value of the product of number of revolutions per unit of time and the number of saw teeth, i.e. 1/xn.
In the past, forced elastic deflection of the flange led to an oscillating movement of the structural flange. The oscillation time or period of the oscillation and the tooth succession time coincide more or less, or the tooth succession time is even greater than the oscillation time. The oscillation time is the reciprocal value of the frequency of this oscillation. Actual and marked resonance phenomena appear during this process.
I have now found by experiment that the stresses and strains resulting from the interaction of such oscillations and the cutting operation considerably shorten the service life of the metal saw.
Furthermore, under these conditions one can only work with limited feed speed which is coordinated with the number of r.p.m. and which can not be too fast. As a result the efficiency of the entire saw apparatus is limited.
This limitation is true also for the level of cutting performance or, energy efficiency which, by way of example, is defined by a quotient which relates the cutting capacity to the motor's expenditure of energy.